Preterm delivery occurs in up to 10% of births and accounts for 75% of neonatal deaths. A greater understanding of the mechanisms of contractile quiescence during normal pregnancy is sorely needed. The general aim of this proposal is to test the hypothesis that basal thin (actin) and thick (myosin) filament regulatory mechanisms are chronically altered during normal and abnormal pregnancy and labor. The specific aims are: (1) To investigate the hypothesis that changes in either the protein levels or phosphorylation levels of the actin binding protein, Caldesmon (CaD) contribute to gestation dependent contractility changes in both a timed pregnant rat model and in human tissue samples; (2) To investigate the hypothesis that changes in Extracellular Regulated Kinase (ERK1/2) signaling contribute to changes: (a) in CaD activity; and/or (b) in the contractility of myometrium during pregnancy and labor in the rat and human; (3) To investigate the hypothesis that regulation of Myosin Phosphatase is involved in gestation-dependent changes in contractility in the rat and human; and (4) To investigate the hypothesis that coordination of signal transduction that leads to gestation-dependent changes in contractility is, at least in part, mediated by the action of the scaffolding protein, caveolin. Because of the limited supply of human tissue, a timed rat model will be used for the detailed mapping of signaling pathways and the planned in vivo drug studies. However, human samples will be collected in parallel and, on a longer time base, will be used to test critical results obtained with the rat tissue. A multidisciplinary approach will be used, combining functional assessment of contractility, biochemical measurements, quantitative confocal microscopy, organ culture, antisense experiments, and in vivo drug treatment to test the above hypotheses. It is hoped that if novel mechanisms can be identified and defined, the pathways involved will represent new potential targets for therapeutic intervention in cases of preterm and dysfunctional labor.